The present invention relates generally to a resin-molded motor and a method of manufacturing it.
A resin-molded motor, such as a compact induction motor commonly used in a home washing machine, comprises a resin-insulated core winding, a stator with a winding, and a rotor accommodated in a resin housing. In the conventional resin-molded motor, as disclosed in Japanese laid-open patent application 79207/1977, a non-magnetic cylindrical member is disposed at each end of a magnetic pole member of the stator and said magnetic pole member and a yoke member are spray-coated with a resin composition to insulate the winding portion of the stator and, at the same time, to secure said cylindrical member to the end face of the stator. After the winding is formed, the whole assembly is covered with a molded resin, i.e. resin-molded, housing.
As described in the above patent literature, the cylindrical member of non-magnetic material which is disposed at each end is intended to prevent the coil end of the winding from passing across the core center and to prevent inflow of the molding resin composition into the rotor segment and the resin coating is intended to bond the members into an integral unit, insulate the stator and secure the punched-out stator members in position.
However, since the cylindrical member has the same inner diameter as said stator members so as to permit insertion of the rotor, the coil end tends to expand outwardly where the primary coil overlaps with the secondary coil so that the ineffective part of the coil is increased to cause such problems as increased electric resistance, increased coil requirements and increased weight. Moreover, unless the outer diameter of the magnetic pole member of the stator is increased, the yoke member cannot be inserted into the magnetic pole member so that the overall size and weight has to be increased.
Furthermore, although the individual stamped-out core members laminated and bonded have been secured in position at the slots by the resin coating, the magnetic pole portions along the inner circumference facing the rotor are interconnected in the form of a ring and, therefore, not secured by the resin coating, with the result that the overall mechanical strength is not sufficient and the resin may crack and cause an insulation failure. Moreover, because of the bridging of magnetic poles, the electrical characteristics of the motor are also unsatisfactory.
It is therefore the object of the present invention to provide a resin-molded motor having improved characteristics and reduced bulk which have been achieved by improvements in the construction of the stator and cylindrical member.